let's take a look and meet lindsay. lindsay has just started first grade. but she's living inside a body that is biologically older than her grandmother's. although her body is aging, her mind is not. >> my mom and i play with the ponies. we read books. we play games. legos, ponies, my drum set, trains, cooking. >> reporter: but all these activities take a toll on lindsay's body. >> every time i run, like at recess at school, my muscles hurt. >> do they? >> yes. the leg ones. not my arm ones. my leg ones. >> really? >> yes. >> reporter: so, every week, she goes to the chiropractor for a checkup. >> got it? okay. here we go. how is your neck feeling today? >> really bad. >> really bad? >> yeah. >> she's 6 years old. she runs and jumps. she has the spine of a 60-year-old or a 70-year-old. there is arthritis forming in the spine. >> ouch. >> reporter: does she ever ask you questions you can't answer? >> if she catches us off-guard, she's asked why does my skin look like this? or something like that. and it takes me a minute. and i tell her, give me a minute so